The present invention relates to a sensor system comprising a radiometric device, a Doppler effect radar device, and means for comparing the signals received through these devices or the information obtained from such signals.
Such sensor systems are employed preferably for detecting metallic targets in a disturbed ambience, with the disturbance being mainly the irregularities of the earth's surface surrounding the target. The difficulty with radar sensors is that the disturbing returns from the ground and the return from the target to be detected may be of the same order of magnitude. This involves the risk of taking a disturbance for a target, or of failing to respond while taking a target for a disturbance.
In the detection of metallic targets by means of radiometric sondes, the experience is utilized that the noise temperature of the ground is generally about 300.degree. K., while metallic objects reflect the temperature of the air or sky which is mostly below 100.degree. K. A target may therefore, be identified by measuring the noise temperature of the target area acquired by the antenna of the radiometric system. Such an acquisition, however, is also responsive to water surfaces which reflect the sky temperature. This entails an inacceptably high chance of false alarms while detecting targets by means of a radiometric sonde.
Other prior art target detecting devices are active or passive optical sensors which, however, are generally impractical since they require favorable weather conditions.
Both radar sensors and radiometric sensors detect metallic targets. However, the false targets causing an erronious return are different in the two methods of detection, so that a combination of the two methods is capable of discriminating true targets from wrong ones by correlation. Such a combined sensor system requires radar equipment as well as a radiometric equipment. With the use of prior art devices, the total expenses therefore rise to a level which is too high in many applications where the space available for the sensor system is limited.